The present invention relates to a communication system using a TDMA (Time-Division Multiple-Access) method and more particularly to a communication system which adapts to different communication environments or provides different communication environments for transmitting and receiving signals.
The highly-advanced information technology era has brought with it the increasing demand for systems and devices allowing users to conduct wireless (radio communication) telephone or data-communications in a variety of situations, e.g., during walking outdoor or moving on a vehicle or working in an office. The present rapid development of infrastructures for various kinds of communication systems such as tele-communications with cordless telephones, portable telephones and local-area networks (LAN) radio-communications makes it possible for any one to communicate with any other person any time at any place.
However, many infrastructures have incompatible systems that require the use of specially designed terminals, preventing terminals from being used in common between the systems. For example, two representatives of TDMA communication systems, i.e., Personal Digital Cellular system (PDC) and Personal Handy-phone system (PHS) are incompatible and use different radio-frequencies, transmission power values, a number of slots per frame, bit rates, methods for coding and decoding audio signals and so on.
The incompatibility of the communications systems requires users to use different devices (PHS, PDC, Pagers, and so on) specially designed for respective systems to make wireless (radio communication) telephone or data-communications during walking from a vehicle or from an office. This is inconvenient for users. A terminal that can realize functions of two different systems may be manufactured with an increased size because it must contain many processing circuits that cannot be commonly used.
Accordingly, the present invention is directed to provide a TDMA communication system which adapts to different communication environments or prepares different communication environments for communications between mobile stations and base stations and allows each mobile terminal to conduct radio-communication at different transmission rates under different environments.
(1) An object of the present invention is to provide a TDMA communication system for executing communications between mobile stations and a base station using a TDMA method, wherein a TDMA format that has a constant time of a frame length and a constant number of bits in each of slots composing a frame is used as a common-use communication data format and each of the mobile and base stations is provided each with a communication device for processing communication signals based on the TDMA format, which device can operate in any one of plural different Communication environments designated by selecting a corresponding one of prepared sets of environmental communication conditions each including a transmission power value, a modulation method, the number of multiplexed signals and an error-correction method.
(2) Another object of the present invention is to provide a TDMA communication system as mentioned (1) above, which is characterized in that communications between the mobile stations and the base station are made by means of radio communication in a selected communication environment with the prepared conditions including additional conditions such as an antenna gain, a diversity method and frequency hopping.
(3) Another object of the present invention is to provide a TDMA communication system as mentioned (1) or (2) above, which is characterized in that priority of the different communication environment conditions are registered in a data base allowing the communication devices to select one of the communication environments according to the preset priority.
(4) Another object of the present invention is to provide a TDMA communication system as mentioned any one of (1) to (3) above, which is characterized in that the plural sets of different communication environment conditions are prepared for at least two of different environments comprising an office communication environment, a walking-speed communication environment, a mobile-running-speed communication environment and a satellite communication environment.
(5) Another object of the present invention is to provide a TDMA communication system as mentioned any one of (1) to (4) above, which is characterized in that the base station generates individually each set of the communication environment conditions and broadcasts the generated environmental information and each mobile station receives the broadcasted information and automatically selects a corresponding one of the prepared sets of the communication conditions according to the received information of communication-environment conditions.
(6) Another object of the present invention is to provide a TDMA communication system as mentioned any one of (1) to (4) above, which is characterized in that any of the prepared sets of the communication conditions can be manually selected and set.
(7) Another object of the present invention is to provide a TDMA communication system as mentioned any one of (1) to (6) above, which is characterized in that equalizing means with an adaptive equalization mode being changed according to a selected one of the communication environments are additionally provided for improving a bit error rate in a fading channel.
(8) Another object of the present invention is to provide a TDMA communication system as mentioned any one of (1) to (7) above, which is characterized in that the system is provided with a data base for controlling whole communication environments of mobile stations communicating with other mobile stations through the base station over a radio channel established between them and the data base is adaptable to changing channel connections from one environment to another different environment.
(9) Another object of the present invention is to provide a TDMA communication system as mentioned any one of (1) to (8) above, which is characterized in that the TDMA format is a format that can be commonly used by a personal handy-phone system (PHS).